U.S. oil prices fell sharply Thursday after a weekly report showed U.S. inventories of petroleum products are already starting to rise now that summer is ending and the lower-demand fall season is near.

Light, sweet crude for October delivery fell 1.4% to close at $67.77 a barrel on the New York Mercantile Exchange. Brent crude, the global benchmark, lost 1% to $76.50 a barrel.

The Energy Information Administration said Thursday that crude-oil inventories fell by 4.3 million barrels last week. And while that data point alone is bullish, the report also showed gasoline and distillates inventories rose by a combined 5 million barrels, and the grand total of crude oil and processed petroleum products rose by a bearish 3.6 million barrels.

“The fundamentals are starting to get a little bit questionable,” said Ric Navy, senior vice president for energy futures at R.J. O’Brien & Associates.

The EIA report also showed U.S. crude oil exports fell by 271,000 barrels a day last week, to 1.5 million barrels a day.

Mr. Navy said Thursday’s report on U.S. oil inventories wasn’t the only factor in oil’s decline, noting overall global demand is also becoming a bigger concern. “There are more clouds as far as economies go, and the tariff disputes are also a factor.”